1. Field of the Invention
The present invention relates to a method for manufacturing an SOI substrate having a so-called silicon-on-insulator (SOI) structure in which a single crystal semiconductor layer is provided on an insulating surface, and a method for manufacturing a semiconductor device having the SOI structure.
2. Description of the Related Art
Integrated circuits in which a semiconductor substrate called a silicon-on-insulator (hereinafter also referred to as “SOI”) having a thin single crystal semiconductor layer on an insulating surface is used instead of a silicon wafer which is manufactured by thinly slicing a single crystal semiconductor ingot have been developed. The integrated circuits using an SOI substrate have attracted attention as integrated circuits with reduced parasitic capacitance between a drain of a transistor and a substrate and improved performance of semiconductor integrated circuits.
As a method for manufacturing an SOI substrate, a hydrogen ion implantation separation method is known (for example, see Patent Document 1). The hydrogen ion implantation separation method is a method in which hydrogen ions are implanted into a silicon wafer to form an embrittled region at a predetermined depth from the surface, and the silicon wafer in which the embrittled region is formed is bonded to the other silicon wafer. Next, heat treatment is performed to cause separation along the embrittled region so that a thin silicon layer is formed on the other silicon wafer. Further, it is necessary to perform heat treatment in an oxidizing atmosphere, form an oxide film on the silicon layer, remove the oxide film, and perform heat treatment at 1000° C. to 1300° C. in order to increase bonding strength.
In addition, a method for forming a single crystal silicon layer over a base substrate made of glass by such a Smart Cut (registered trademark) method has been proposed (for example, see Patent Document 2).
The silicon layer formed in such a manner is in a state where crystal defects remain on a surface of and in the silicon layer due to the ion irradiation step for forming the embrittled region and the separation step, and the planarity of the surface significantly deteriorates. Further, if separation is not smoothly conducted along the embrittled region, there arise problems such as a rough surface, variation in thickness, and generation of minute cracks of the silicon layer.
Removal of crystal defects of a silicon layer can be achieved by heating at a temperature of 1000° C. or higher; however, such a high temperature process cannot be utilized for removal of the crystal defects of the silicon layer which is attached to the glass substrate having a strain point of 700° C. or lower. Thus, as disclosed in Patent Document 3, there has been an attempt to irradiate a silicon layer with a laser beam to recrystallize the silicon layer, so that crystal quality of the silicon layer is improved (see Patent Document 3).
[Citation List]
    [Patent Document 1] Japanese Published Patent Application No. 2000-124092    [Patent Document 2] Japanese Published Patent Application No. 2002-170942    [Patent Document 3] Japanese Published Patent Application No. 2005-252244